Interleukin 22 (IL-22) is a member of the IL-10 family or IL-10 superfamily (including IL-19, IL-20, IL-24, and IL-26) of cytokines, a class of potent regulators of cellular inflammatory responses. It shares the use of IL-10R2 in cell signaling with other members of this family, IL-10, IL-26, IL-28A/B, and IL-29.IL-22 is produced by activated DCs and T cells and initiates the innate immune response against pathogenic bacteria, especially those originating from epithelial cells, such as respiratory and intestinal epithelial cells. Patients with psoriasis exhibit strongly elevated plasma levels of IL-22, which correlates with the severity of the disease. In hepatitis mediated by concomitant cutanea lectin A (ConA)-induced T cells, IL-22 may play a protective role as a survival factor for hepatocytes. In contrast to IFN-γ and IL-17, large amounts of IL-22 are present in the blood of patients with Crohn’s disease.